Downshift control for automotive automatic transmission

Abstract

An automotive automatic transmission control apparatus is provided which works to increase the power of an engine in response to a request to down-shift the gear of an automatic transmission for developing the engine braking. The control apparatus includes a fail-safe circuit working to stop increasing the power of the engine when a defect in operation of a transmission hydraulic control circuit is detected after the hydraulic control circuit starts to control the hydraulic pressures to achieve the downshift of the automatic transmission. This eliminates or alleviates a problem, such as unwanted acceleration of the vehicle during the control of the downshift in the transmission.

Description

CROSS REFERENCE TO RELATED DOCUMENT [0001] The present application claims the benefit of Japanese Patent Application No. 2004-239811 filed on Aug. 19, 2004, the disclosure of which is incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Technical Field of the Invention [0003] The present invention relates generally to an automotive automatic transmission controller equipped with a feature to increase an engine power for minimizing a shift shock occurring during downshift control executed according to a driver's deceleration intention to develop the engine braking. [0004] 2. Background Art [0005] Most modern automotive automatic transmissions are designed to switch between hydraulic control lines to establish engagement and disengagement of frictional elements such as clutches and brakes selectively for achieving a desired one of speeds. When the accelerator of the vehicle is released fully during running on a downhill, but the engine braking is insufficient, the d...

AI Technical Summary

Benefits of technology

[0012] It is another object of the invention to provide an improved structure of an automatic transmission controller designed to eliminate or alleviate a problem, such as unwanted acceleration of a vehicle during control of a downshift in the transmission executed in response to a request from a driver of the vehicle, which arises from, for example, a failure in operation of a hydraulic pressure control device.

[0013] According to one aspect of the invention, there is provided an automatic transmission control apparatus which may be employed in automotive vehicles. The automatic transmission control apparatus comprises: (a) a hydraulic control circuit which controls hydraulic pressures to be applied to a plurality of frictional elements such as clutches and brakes of an automatic transmission joined to an engine to selectively achieve engagement and disengagement of the frictional elements for establishing a required speed of the automatic transmission; (b) a defect detector working to detect a defect of the hydraulic control circuit; (c) an engine output increasing circuit designed to perform engine output increasing control to increase an output of the engine upon a downshift of the automatic transmission to develop engine braking in response to a request from an operator to decelerate a speed of the automatic transmission, the engine output increasing circuit initiating the engine output increasing control within an interval between start to control the hydraulic pressures through the hydraulic control circuit to achieve the downshift and start of an actual shift in speed of the automatic transmission; and (d) a fail-safe circuit working to stop the engine output increasing control immediately when the defect detector detects the defect of the hydraulic control circuit after the hydraulic control circuit starts to control the hydraulic pressures to achieve the downshift of the automatic transmission. This alleviates a problem such as unwanted acceleration of a vehicle during hydraulic control of a downshift in the transmission executed in response to a request from a driver of the vehicle.

Problems solved by technology

This may cause the time required for the downshift to be increased, thus giving rise to a delay in the engine braking or inertia torque arising from the increased speed of the engine to appear as braking torque, which results in an instantaneous increase in the engine braking, leading to a large-scale shift shock.

A rapid rise in torque transmitted through the frictional elements of the automatic transmission under hydraulic control will result in a quick rise in speed of the engine, so that the downshifting time decreases, but however, the braking torque increases excessively, thus resulting in a more increase in the shift shock.

Therefore, if a defect occurs in a hydraulic controller working to control the torque transfer capacity, it will result in an error in dropping the hydraulic pressure acting on the off-going frictional element and a difficulty in achieving the downshift.

For instance, in a case of a 4-3 downshift, the power of the engine is increased while a 4th speed gear ratio is locked without developing the engine braking, thus resulting in undesirable acceleration of the vehicle during the hydraulic control for the downshift.

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